1. Field of the Invention
The present invention generally relates to electron beam pumped lasers, and particularly to electron beam pumped lasers such as those that provide a light source for projection television.
2. Description of Related Art
Projection televisions for consumer applications utilize a white light source such as a xenon or halogen lamp, dichroic filters to separate the red, green and blue light components, and a spatial light modulator (SLM) to modulate the red, green, and blue light. The modulated light is then projected through appropriate optics to generate an image. A number of SLM technologies may be used, such as liquid crystal panels, digital micro-mirrors, and grating light valves, for example. Alternative light sources such as LEDs or laser diodes are either impractical or non-existent for consumer projection televisions because they require too much power for consumer use and are too expensive. For example, the large light emitting surfaces of multiple LEDs make it difficult and expensive to optically capture the emitted light and difficult and expensive to modulate it with an SLM.
An alternative light source, now under development, utilizes one or more laser cathode ray tubes (“Laser-CRTs”) to generate red, green or blue laser light. The different colors can then be combined, modulated and projected to generate an image.
Prior art Laser-CRTs include a laser faceplate in a conventional cathode ray tube. The laser faceplate comprises a laser medium sandwiched between a highly reflective mirror and a partially reflective mirror in which a scanning electron beam bombards the highly reflective mirror. The partially reflective mirror may include a stack of quarter-wave alternating layers of Al2O3 and TiO2 for example. An electron gun generates an electron beam, which is deflected and focused by electromagnets to impinge upon a desired location on the laser faceplate.
In prior art laser CRTs, the electron beam emitted from the electron gun travels a longitudinal direction toward the laser faceplate at the opposite end of the tube. The electron beam is deflected along the horizontal and vertical axis as it passes between the deflection coil and the laser faceplate, to impinge upon a desired location on the faceplate. In a fraction of a second, the electron beam is scanned across all the screen pixels, thereby creating a raster scan similar to conventional CRT operation. The electron gun may be modulated as the beam is scanned across the faceplate, thereby creating an image.